At least 33 people, including three fire fighters, were killed when the roof of a supermarket collapsed during rush hour in the Latvian capital of Riga. Hours later, rescue workers are still searching through the rubble, asking family members and friends to call the cell phones of the missing to help locate their bodies.

An estimated 5,300 square feet of the roof collapsed during the disaster, Latvia's worst since gaining independence from the Soviet Union in 1991. Twenty minutes later, a second part of the roof fell in, killing the three fire fighters. Many of the victims tried to escape after the first collapse, but were trapped in the store by its electronic doors.

"It is clear that there has been a problem with fulfillment of construction requirements," Latvia's interior minister, Rihards Kozlovskis, told Latvian TV about the store, a Maxima supermarket that reportedly won an architecture award in 2011.

One witness who escaped the store unharmed described the ordeal to the BBC.

"I was taken down by shelving falling on me, which skimmed my shoulder and forced me to the ground but I was still able to move," Paul Tribble, a British pilot, told the BBC."There were torrents of water coming down off the roof. We headed into the back of the supermarket, the aisles were covered in produce and concrete and people lying on the floor."

Tribble also said that a crane had been loading sand and other building materials on the roof for weeks, reportedly as part of the store's plan to build a rooftop garden.

"The police have started the investigation already," Prime Minister Valdis Dombrovskis said after visiting the scene."The criminal process has started about violating building standards."